The use of various bleaching agents to remove color of cellulose, both during refining and purification, and also of cellulose esters is well known in the art. For instance, sodium hypochlorite, oxygen and free chlorine are well-known color reducing or bleaching agents for cellulose, especially cellulose derived from wood sources. Potassium permanganate (KMnO.sub.4) or hydrogen peroxide (H.sub.2 O.sub.2) has been used as a bleaching agent for cellulose esters prepared by normal acetylation and hydrolysis procedures. Potassium permanganate, although being an effective bleaching agent for cellulose esters, poses certain environmental pollution problems and the resulting liberated manganese must be recovered and disposed of. The use of either hydrogen peroxide or persulfate as a bleaching agent requires larger than desired quantities to be effective and thus is not normally used commercially.
The use of higher than normal temperatures, normal temperature being from about 40.degree. C. to about 50.degree. C., for acetylation and hydrolysis of cellulose esters provides a more uniform, higher quality product from lower quality, less expensive cellulose raw materials. However, the higher process temperatures, from about 80.degree. C. to about 150.degree. C., impart substantial color to the cellulose ester and require an effective bleaching agent to obtain acceptably low color ester. Hydrogen peroxide or persulfates used alone are not satisfactory bleaching agents in the higher than normal temperature process, i.e. from about 80.degree. C. to about 150.degree. C., owing to the large amount of bleaching agent required and its deleterious effect on cellulose ester molecular weight, i.e. high concentrations greater than 0.5% of either hydrogen peroxide or persulfate will undesirably reduce the molecular weight, thereby causing a loss of physical properties such as strength and toughness; e.g., in a molded plastic or extruded fiber. However, we have discovered that the use of a combination of hydrogen peroxide and persulfate as a bleaching agent for cellulose acetate is unexpectedly effective at low concentrations, i.e. about 0.2 to about 0.4 pphr (parts per hundred parts resin), for removing color without concurrent loss of polymer molecular weight.